NPPB and hydrops fetalis: Although previous studies have indicated that plasma concentrations of ANP and NT-proANP are strongly correlated to NT-proBNP levels,38 Reginauld et al. suggest that ANP and BNP may be differentially regulated in HF with the possible existence of a ANP-deficient subgroup among HF patients.39 The presence of an alternate mechanism of regulation between ANP and BNP is also supported by the increased susceptibility to degradation of ANP compared to BNP by neprilysin.40,41